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France's Foreign Ministry is warning French travelers of a high terrorism risk in Britain, asking them to be watchful in public transport and busy tourist areas across the English Channel.

A message posted on the ministry's Web site late Tuesday said British authorities have warned that "the level of terrorist threat is very high in the United Kingdom, and the risk of an attack is very likely." The ministry said France wanted to pass those concerns on to French citizens, many of whom live in Britain or travel there frequently.

France has not issued any recent warnings for other countries in Europe, though officials have repeatedly insisted that the threat is high in France as well and have boosted security at busy tourist sites such as Notre Dame Cathedral and the Eiffel Tower in Paris.

France and Britain are among many European countries that have stepped up terrorism alert vigilance recently. Germany, meanwhile, says it remains watchful but that there is no reason to be "alarmist."

Security officials have said terrorists may be plotting attacks in Europe with assault weapons on public places, similar to the deadly 2008 shooting spree in Mumbai, India. European officials have provided no details about specific targets.

The French warning was issued before gunmen fired a rocket at a convoy carrying Britain's No. 2 diplomat in Yemen on Wednesday, wounding four people amid heightened fears about al-Qaida influence in the Arabian Peninsula country.

There was no immediate claim of responsibility for the attack. In a separate incident in Yemen the same day, a gunman fatally shot a French citizen.

Pascal Omnes, a spokesman for French engineering firm SPIE, said the French citizen killed was employed by the company as a logistics and procurement manager as part of its contract with Austrian oil and gas company OMV.

SPIE, which in Yemen has about 100 employees who come from about 20 countries, has instructed all nonessential personnel to return home as soon as possible — an order affecting about 15 to 20 people, Omnes said. He said the company has also raised its internal security alert level in the country.

This weekend, the U.S. State Department advised American citizens living or traveling in Europe to take more precautions about their personal security. Britain's Foreign Office in turn warned travelers to France and Germany of a high terror threat.

France's warning did not mention Germany. That was because the Germans, unlike the British, have not expressed such serious concerns about a terror threat inside their territory, said a French diplomatic official speaking on condition of anonymity because of office policy.

Germany's Interior Minister Thomas de Maiziere has said security forces in Germany remain vigilant due to the ongoing "high abstract danger" of a terror threat, but he has insisted there was "no reason to be alarmist."

The United States believes a cell of Germans and Britons are at the heart of a terror plot against European cities, a plan they link to al-Qaida leader Osama bin Laden. Pakistani officials said this week that eight German militants were killed in a U.S. missile strike in Pakistan.

German Foreign Minister Guido Westerwelle said his nation is trying to clarify the situation.

"We don't have reliable information at this point," he said.

The Interior Minister Thomas de Maiziere told Deutschlandfunk radio he was astonished that militants killed by a drone were identified so swiftly.

"What I find particularly astounding is that this attack allegedly was carried out by unmanned drones the day before yesterday in a region that is difficult to reach, and at the same time they find identity papers," he said. "That doesn't go together, we first need to clarify this."